Phonak’s Tyler Hamilton, who won the Olympic time trial gold medal last month, said he was totally innocent of the charge of blood doping after it was revealed on Tuesday he had become the first athlete to test positive for it.

The 33-year-old faces a two year ban after testing positive after winning the Tour of Spain's eighth stage time trial on September 11 and he pulled out of the Tour six days later apparently due to stomach problems. Hamilton's Swiss Phonak team confirmed the positive result and news of the second sample is expected within 48 hours.

However Hamilton insisted he was innocent at a hastily assembled press conference at the town of Regensdorf near Zürich.

"This affair has been like a thunderbolt," admitted the American. "I am absolutely devastated to have to be here this evening as are my family, my friends and teammates. But I can assure you of one thing I am 100 percent innocent.

"I am not going to risk my life and that of my wife with a blood transfusion, there must have been some kind of mistake," he added.

Hamilton said that he would never dope and if he felt he had to he would prefer to retire.

"I am accused of taking someone else's blood, but anybody who knows me would accept that I would never do such a thing,” he said. "I know what I put into my body and what I don't. Cycling is very important for me but not everything. If was to think I had to do something like that I would rather put my bike away."

Dick Pound, head of the World Anti-Doping Agency (WADA), declared himself satisfied with the news.

"If it stays positive, then it will the first ever case of this form of doping being detected," he said in Montreal where he was attending WADA's executive committee meeting.

Phonak director Alvaro Pino said he was confident about Hamilton's innocence. Live on Spanish television while driving a car during the 16th stage of the Tour of Spain, Pino said: "Last night (Monday), he (Hamilton) said 'you can sleep soundly.'”

"I believe him. He is an intelligent guy who would not take the risk of having a blood transfusion,” Pino added. “The test result is not yet conclusive. I can't tell you any more."

The UCI has for the first time used a method to detect blood-doping which has been used in legal medicine for paternity tests. The tests were developed in Sydney and are now used by two accredited laboratories in Athens and Lausanne, Switzerland.

The test can identify different groups of red blood cells which thereby determine conclusively whether blood-doping has taken place.

Usually an athlete will withdraw blood before reintroducing it before an event to increase oxygen-carrying capacity to the muscles hence enhancing his performance.

Till now blood doping, suspected of being used in athletics for the last 30 years, was undetectable.

Hamilton has had an eventful, up-and-down year, injuring his back in a crash which led to his retirement during the 13th stage of the Tour de France in July but bounced back to win the time-trial in Athens. Hamilton famously raced three weeks to finish fourth in the 2003 Tour de France after breaking his collarbone in the first stage.

Hamilton dominated the Tour of Romandy this year to such an extent he was considered among an elite group of riders as a possible Tour de France champion. However his Tour challenge faltered following a fall at Angers.

For Phonak, it was the second doping affair to hit them during the year following the positive test for blood-boosting drug EPO by Switzerland's Oscar Camenzind. Camenzind was axed by the team and he retired from the sport before being suspended by the Swiss Olympic committee for two years.